Possible to write XMP sidecar for .AVI files only?

[Info Munky]

I'm experimenting with Digikam tags (keywords) on the video files in my 
collection, and can see that tags are written to the IPTC container for 
.MOV files, but where I have some older .AVIs, as far as I can see the 
tags are only in the Digikam database, and not written to the file in 
any way.

Have read a bit about XMP sidecars, and was wondering whether its 
possible to generate (automatically) XMP sidecar for a specific MIME 
type only (ie .AVI) as I don't want to globally generate XMP for JPG, 
RAW, MOV etc.

Is this possible, or is there any alternative approach (apart from MIME 
type conversion)?